Yeah, I had always thought that the newer valve poppet springs were stiffer, but had no way to quantify the difference.Though it IS weird that sometimes the rifle will heal itself............other times it will make itself ill.........Have you tested a spring in the 717 screw in valve that many sell as a direct replacement for the 880 screw in??(I have never got one of those to work without modifying the sear a bit....the stem is effectively too long and the valve doesn't open far enough to achieve a good air dump.This is due to the poppet bulb being longer than the old 880 poppet nose.......